The use of polyurethane-based compositions for golf ball layers has increased over the last few decades. In particular, polyurethane-based compositions, which are formed from a prepolymer of an isocyanate and a polyol that is cured with a diol or amine curing agent, have been used in golf ball cover layers due to the durability of the material and the soft “feel” when struck with a club.
A demand for shorter turn around and processing times, however, has led golf ball manufacturers to explore other materials that provide the beneficial properties of a polyurethane-based composition with a faster cure cycle. For example, polyurea-based compositions, which are formed from a prepolymer of isocyanate and polyamine that has been cured with an amine-terminated curing agent, have been proposed for use in golf ball layers as a potential replacement or substitute for polyurethane golf ball layers because of the extremely fast reaction rate. In addition, because the system requires no catalyst, the reaction mechanism is extremely reliable. Moreover, because polyurea compositions are typically 100 percent solids, no volatile organic compounds are emitted (at least with respect to coating applications).
Due to the high and autocatalytic activity of the amine with the isocyanate, however, the reaction rate may proceed too quickly to control during manufacturing. For example, unhindered primary diamines are generally fast reacting. In addition, aliphatic amines react more quickly than aromatics of lower basicity, since there is not any significant steric hindrance. In fact, the ortho position substituents of aromatic isocyanates strongly reduce the reactivity. This is especially apparent in two-component polyurea coating systems, which leads to the need for high pressure equipment, preheated products for reduced viscosity, heated hoses, and impingement mixing for fast spray application of the rapidly setting material.
As such, secondary amines with steric hindrance, such as UNILINK® 4200 (commercially available from UOP of Des Plaines, Ill.), halogen-containing curatives, and sulfur-containing curatives have been used in an attempt to slow down the reaction between the isocyanate and the amine-terminated curing agent in these two-component coating systems. In addition, adding propylene carbonate has been shown to reduce the reactivity of the system, as well as improve flow and wetting properties. This type of reaction rate-modifying solution appears to be highly limited to the coating systems.
Thus, there remains a need in the golf ball art for a way to modify the reaction rates of polyurethane-based and polyurea-based compositions for use in structural golf ball layers. In fact, it would be advantageous to provide a way to modify the reaction rate of the isocyanate groups of the prepolymer with the amine groups in the curing agent in order to increase efficiency and predictability in production without the use of halogen groups, sulphur substituted, or sterically hindered secondary diamines. The present invention is directed to such a solution.